1. Field of the Invention
The invention relates to flotation devices and in particular to an injector for mixing air and another fluid, such as a fiber suspension, in a flotation device.
2. Description of Related Technology
An injector having a variable cross section for use in a flotation device is known from DE 34 01 161 (corresponding to Linck et al., U.S. Pat. No. 4,620,926 issued Nov. 4, 1986). Considerable turbulence is produced by step-wise changes in the cross-sectional area of the device. As a result, relatively fine air bubbles are mixed with a liquid suspension flowing therethrough. Air is introduced from a side of the device upstream of the step-wise changes.
On the other hand, mixing devices are known for various liquid components in which plates with irregular, substantially ridge-shaped surfaces, inclined at a certain angle to the direction of flow, are disposed so that the ridges of neighboring plates crisscross. A mixing device disclosed in DE 22 05 371 (corresponding to Huber, U.S. Pat. No. 3,785,620 issued Jan. 15, 1974 and Huber et al., U.S. Pat. No. 3,871,624 issued Mar. 18, 1975) is provided with spherical caps of the ridges of neighboring plates which touch one another. A plurality of parallel plates are provided in a housing perpendicular to the direction of flow. The housing has a circular cross section. To improve the mixing action, the plates are preferably disposed in packets in the housing so that plates or neighboring packets of plates butting against one another always have opposite angles of inclination with respect to the longitudinal axis (flow direction) of the mixer housing.
Furthermore, there are flotation devices such as those disclosed in DE 36 14 933 (corresponding to Schweiss et al., U.S. Pat. No. 4,726,897 issued Feb. 23, 1988) for the treatment of waste paper suspensions in which only a few injectors are used for aerating the suspension. Preferably, these injectors are oriented vertically so that they are immersed into the suspension from the top thereof. However, there are also devices in which the injectors are disposed horizontally, that is, they provide horizontal inflow of a suspension.
DE 37 41 843 discloses a device for mixing liquids with gases having an annular flow channel with projections extending into it. The device uses annular channels only and is unsuitable for large flotation installations with high throughputs for aerating pulp suspensions.